Photocatalytic CO2-to-CH4 Conversion with Ultrahigh Selectivity of 95.93% on S-Vacancy Modulated Spatial In2S3/In2O3 Heterojunction

Photocatalytic conversion of CO2 to methane faces challenges due to the stability of CO2, unpredictable intermediates, and complex electron transfer steps. Herein, a spatial In2S3/In2O3 heterojunction with abundant S vacancies (ISIO(V-S)) is obtained through facile Polyvinylpyrrolidone (PVP) treatment to reach a methane yield of 16.52 mu mol<middle dot>g(-1)<middle dot>h(-1) with a selectivity of 95.93%, which is the highest among reported In2S3 and In2O3 based catalysts. The work function (W-f), differential charge density, and Kelvin Probe Force Microscopy (KPFM) results confirm that S vacancies strengthen the built-in electric field (BEF) of In2S3/In2O3 (ISIO) heterojunctions, improving carrier separation. Density functional theory (DFT) calculations reveal that S vacancies induce electron redistribution, facilitating adsorption and activation of CO2 and *CO intermediate, thus promoting hydrogenation to yield *CHO. The reaction pathway of photocatalytic CO2 reduction is revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Gibbs free energy (Delta G). The S vacancies modify electronic orbitals and the highest occupied molecular orbital (HOMO) of In atom, resulting in a stronger interaction between the catalyst and *CHO, which reduces Delta G(*CHO) and regulates the selectivity of CH4. This study paves a new avenue for the design of photocatalysts with highly selective reduction of CO2 to CH4 through defect engineering.